This is the ONLY way to beat him, its very dangerous and believe me, not even Totsuka Blade will work.
So the only way is
Flying Thunder God.
We have seen Tsunade mentioning this but I'm not sure if she was refering to Madara, but its very reasonable to be him, here is why.
Keeping in mind, Minato is sealed with the Shingami, according to Genma, as a Hokage Guard and Flying Thunder God user, it is very important to place FTG on the Hokage.
Meaning Minato would obviously still have a seal of FTG on himself.
So how is this gonna beat Madara?
IF Madara is marked with FTG and teleported to Minato (Which resides with Shinigami) theres a chance he could be sealed within the Shingami without even using the Shingami Seal Jutsu.
So how is this gonna happen?
Naruto is going to have to learn FTG, he will then also carry his father's legacy within this time. Making it a great plot.
What do you think?